# New Features* Language core features- Keyword arguments, which give flexibility to API design- Module#prepend, which is a new way to extend a class- A literal %i, which creates an array of symbols easily- __dir__, which returns the dirname of the file currently being executed- The UTF-8 default encoding, which make many magic comments omissible* Built-in libraries- Enumerable#lazy and Enumerator::Lazy, for (possibly infinite) lazy stream- Enumerator#size and Range#size, for lazy size evaluation- #to_h, which is a new convention for conversion to Hash- Onigmo, which is a new regexp engine (a fork of Oniguruma)- Asynchronous exception handling API* Debug support- DTrace support, which enables run-time diagnosis in production- TracePoint, which is an improved tracing API* Performance improvements- GC optimization by bitmap marking- Kernel#require optimization which makes Rails startup very fast- VM optimization such as method dispatch- Float operation optimization